Initialized empty numpy array is not really empty (contains zeros)

Question

In order to store many 3D points coordinates tuples in a numpy.ndarray I initialize an empty numpy array before entering a loop for each of some features.

To do so, I currently do this before entering the loop:

import numpy as np
pointsarrray = np.empty((1,3))

but this results in an array which is all but empty:

array([[  5.30498948e-315,   0.00000000e+000,   7.81250000e-003]])

When filling pointsarray in my loop after, I do this:

pointsarray = np.vstack((pointsarray, [np.array(myPoint)]))

(it also works with np.append)

and I finally need to delete the first line of the array after exiting the loop because this first line always contains the values from the initialization step!

It's not a big deal but I wonder if there is a cleaner way to achieve a really empty array, I mean; with nothing inside it (it shows 1 row yet, I can not figure out why) but at the right dimensions?

Answer 1

You need the shape to be (0, 3) so you have the correct number of columns to stack but have actually no data inside:

import numpy as np
pointsarrray = np.empty((0,3))

pointsarrray
# array([], shape=(0, 3), dtype=float64)